I made a suggestion to them a while ago, via e-mail.
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Just a puny, tiny, teensy weensy suggestion here.
But letting parties form outside of gates, would be nice.
This way, instead of sending invites and crap after a run is over, you just need to jump back on the platform and go down when everyone has clicked ready.
An LFG crystal thing or something that appears at Crossroads and at the end of levels, will let you diverge without having to leave to Haven just to be invited or join another group. Just go to the crystal, click the group you want to join, go in. It will also allow you to accept invites from other parties who might need you temporarily before returning.
It let's you see all the public parties in progress and gives you a choice to join them, lets you see the gates they're in and all that business.
This way, people looking for specific things will be able to find each other without spamming zone chat, having multiple Havens won't be such an issue down the road and nobody can accidentally join pugs from the gates, because gates are purely dungeon starting places for pre-formed groups or whatever.
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The infrastructure for this already exists within the game, it's just one small step to allow for larger populations of people to co-operate.
All of the existing methods of joining a party would still be there too, like friends list invitation and starting from a gate, this would just make partying a lot more freeform.

It would also mean, if there was a multiplayer only dungeon and somebody disconnected or had to leave, somebody looking to join was only a few clicks away if another friend wasn't available, etc.